// © 2016 and later: Unicode, Inc. and others.
// License & terms of use: http://www.unicode.org/copyright.html
/*********************************************************************
 * Copyright (C) 2000-2014, International Business Machines
 * Corporation and others. All Rights Reserved.
 *********************************************************************
 */

package com.ibm.icu.util;

import com.ibm.icu.impl.CalendarAstronomer;
import com.ibm.icu.impl.CalendarCache;
import com.ibm.icu.text.DateFormat;
import com.ibm.icu.util.ULocale.Category;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.util.Date;
import java.util.Locale;

/**
 * <code>ChineseCalendar</code> is a concrete subclass of {@link Calendar} that implements a
 * traditional Chinese calendar. The traditional Chinese calendar is a lunisolar calendar: Each
 * month starts on a new moon, and the months are numbered according to solar events, specifically,
 * to guarantee that month 11 always contains the winter solstice. In order to accomplish this, leap
 * months are inserted in certain years. Leap months are numbered the same as the month they follow.
 * The decision of which month is a leap month depends on the relative movements of the sun and
 * moon.
 *
 * <p>All astronomical computations are performed with respect to a time zone of GMT+8:00 and a
 * longitude of 120 degrees east. Although some calendars implement a historically more accurate
 * convention of using Beijing's local longitude (116 degrees 25 minutes east) and time zone
 * (GMT+7:45:40) for dates before 1929, we do not implement this here.
 *
 * <p>Years are counted in two different ways in the Chinese calendar. The first method is by
 * sequential numbering from the 61st year of the reign of Huang Di, 2637 BCE, which is designated
 * year 1 on the Chinese calendar. The second method uses 60-year cycles from the same starting
 * point, which is designated year 1 of cycle 1. In this class, the <code>EXTENDED_YEAR</code> field
 * contains the sequential year count. The <code>ERA</code> field contains the cycle number, and the
 * <code>YEAR</code> field contains the year of the cycle, a value between 1 and 60.
 *
 * <p>There is some variation in what is considered the starting point of the calendar, with some
 * sources starting in the first year of the reign of Huang Di, rather than the 61st. This gives
 * continuous year numbers 60 years greater and cycle numbers one greater than what this class
 * implements.
 *
 * <p>Because <code>ChineseCalendar</code> defines an additional field and redefines the way the
 * <code>ERA</code> field is used, it requires a new format class, <code>ChineseDateFormat</code>.
 * As always, use the methods <code>DateFormat.getXxxInstance(Calendar cal,...)</code> to obtain a
 * formatter for this calendar.
 *
 * <p>References:
 *
 * <ul>
 *   <li>Dershowitz and Reingold, <i>Calendrical Calculations</i>, Cambridge University Press, 1997
 *   <li>The <a href="http://www.tondering.dk/claus/calendar.html">Calendar FAQ</a>
 * </ul>
 *
 * <p>This class should not be subclassed.
 *
 * <p>ChineseCalendar usually should be instantiated using {@link
 * com.ibm.icu.util.Calendar#getInstance(ULocale)} passing in a <code>ULocale</code> with the tag
 * <code>"@calendar=chinese"</code>.
 *
 * @see com.ibm.icu.util.Calendar
 * @author Alan Liu
 * @stable ICU 2.8
 */
public class ChineseCalendar extends Calendar {
    // jdk1.4.2 serialver
    private static final long serialVersionUID = 7312110751940929420L;

    // ------------------------------------------------------------------
    // Developer Notes
    //
    // Time is represented as a scalar in two ways in this class.  One is
    // the usual UTC epoch millis, that is, milliseconds after January 1,
    // 1970 Gregorian, 0:00:00.000 UTC.  The other is in terms of 'local
    // days.'  This is the number of days after January 1, 1970 Gregorian,
    // local to Beijing, China (since all computations of the Chinese
    // calendar are done in Beijing).  That is, 0 represents January 1,
    // 1970 0:00 Asia/Shanghai.  Conversion of local days to and from
    // standard epoch milliseconds is accomplished by the daysToMillis()
    // and millisToDays() methods.
    //
    // Several methods use caches to improve performance.  Caches are at
    // the object, not class level, under the assumption that typical
    // usage will be to have one instance of ChineseCalendar at a time.

    /** The zone used for the astronomical calculation of this Chinese calendar instance. */
    private TimeZone zoneAstro;

    /**
     * Cache that maps Gregorian year to local days of winter solstice.
     *
     * @see #winterSolstice
     */
    private transient CalendarCache winterSolsticeCache = new CalendarCache();

    /**
     * Cache that maps Gregorian year to local days of Chinese new year.
     *
     * @see #newYear
     */
    private transient CalendarCache newYearCache = new CalendarCache();

    /**
     * True if there is a leap month between the Winter Solstice before and after the current
     * date.This is different from leap year because in some year, such as 1813 and 2033, the leap
     * month is after the Winter Solstice of that year. So this value could be false for a date
     * prior to the Winter Solstice of that year but that year still has a leap month and therefor
     * is a leap year.
     *
     * @see #computeMonthInfo
     */
    private transient boolean hasLeapMonthBetweenWinterSolstices;

    // ------------------------------------------------------------------
    // Constructors
    // ------------------------------------------------------------------

    /**
     * Construct a <code>ChineseCalendar</code> with the default time zone and locale.
     *
     * @stable ICU 2.8
     */
    public ChineseCalendar() {
        this(TimeZone.getDefault(), ULocale.getDefault(Category.FORMAT), CHINA_ZONE);
    }

    /**
     * Construct a <code>ChineseCalendar</code> with the give date set in the default time zone with
     * the default locale.
     *
     * @param date The date to which the new calendar is set.
     * @stable ICU 4.0
     */
    public ChineseCalendar(Date date) {
        this(TimeZone.getDefault(), ULocale.getDefault(Category.FORMAT), CHINA_ZONE);
        setTime(date);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> with the given date set in the default time zone
     * with the default <code>FORMAT</code> locale.
     *
     * @param year The value used to set the calendar's {@link #YEAR YEAR} time field.
     * @param month The value used to set the calendar's {@link #MONTH MONTH} time field. The value
     *     is 0-based. e.g., 0 for January.
     * @param isLeapMonth The value used to set the Chinese calendar's {@link #IS_LEAP_MONTH} time
     *     field.
     * @param date The value used to set the calendar's {@link #DATE DATE} time field.
     * @see Category#FORMAT
     * @stable ICU 4.0
     */
    public ChineseCalendar(int year, int month, int isLeapMonth, int date) {
        this(year, month, isLeapMonth, date, 0, 0, 0);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> with the given date and time set for the default
     * time zone with the default <code>FORMAT</code> locale.
     *
     * @param year the value used to set the {@link #YEAR YEAR} time field in the calendar.
     * @param month the value used to set the {@link #MONTH MONTH} time field in the calendar. Note
     *     that the month value is 0-based. e.g., 0 for January.
     * @param isLeapMonth the value used to set the {@link #IS_LEAP_MONTH} time field in the
     *     calendar.
     * @param date the value used to set the {@link #DATE DATE} time field in the calendar.
     * @param hour the value used to set the {@link #HOUR_OF_DAY HOUR_OF_DAY} time field in the
     *     calendar.
     * @param minute the value used to set the {@link #MINUTE MINUTE} time field in the calendar.
     * @param second the value used to set the {@link #SECOND SECOND} time field in the calendar.
     * @see Category#FORMAT
     * @stable ICU 4.0
     */
    public ChineseCalendar(
            int year, int month, int isLeapMonth, int date, int hour, int minute, int second) {
        this(TimeZone.getDefault(), ULocale.getDefault(Category.FORMAT), CHINA_ZONE);

        // The current time is set at this point, so ERA field is already
        // set to the current era.

        // Then we need to clean up time fields
        this.set(MILLISECOND, 0);

        // Then, set the given field values.
        this.set(YEAR, year);
        this.set(MONTH, month);
        this.set(IS_LEAP_MONTH, isLeapMonth);
        this.set(DATE, date);
        this.set(HOUR_OF_DAY, hour);
        this.set(MINUTE, minute);
        this.set(SECOND, second);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> with the given date set in the default time zone
     * with the default <code>FORMAT</code> locale.
     *
     * @param era The value used to set the calendar's {@link #ERA ERA} time field.
     * @param year The value used to set the calendar's {@link #YEAR YEAR} time field.
     * @param month The value used to set the calendar's {@link #MONTH MONTH} time field. The value
     *     is 0-based. e.g., 0 for January.
     * @param isLeapMonth The value used to set the Chinese calendar's {@link #IS_LEAP_MONTH} time
     *     field.
     * @param date The value used to set the calendar's {@link #DATE DATE} time field.
     * @see Category#FORMAT
     * @stable ICU 4.6
     */
    public ChineseCalendar(int era, int year, int month, int isLeapMonth, int date) {
        this(era, year, month, isLeapMonth, date, 0, 0, 0);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> with the given date and time set for the default
     * time zone with the default <code>FORMAT</code> locale.
     *
     * @param era the value used to set the calendar's {@link #ERA ERA} time field.
     * @param year the value used to set the {@link #YEAR YEAR} time field in the calendar.
     * @param month the value used to set the {@link #MONTH MONTH} time field in the calendar. Note
     *     that the month value is 0-based. e.g., 0 for January.
     * @param isLeapMonth the value used to set the {@link #IS_LEAP_MONTH} time field in the
     *     calendar.
     * @param date the value used to set the {@link #DATE DATE} time field in the calendar.
     * @param hour the value used to set the {@link #HOUR_OF_DAY HOUR_OF_DAY} time field in the
     *     calendar.
     * @param minute the value used to set the {@link #MINUTE MINUTE} time field in the calendar.
     * @param second the value used to set the {@link #SECOND SECOND} time field in the calendar.
     * @see Category#FORMAT
     * @stable ICU 4.6
     */
    public ChineseCalendar(
            int era,
            int year,
            int month,
            int isLeapMonth,
            int date,
            int hour,
            int minute,
            int second) {
        this(TimeZone.getDefault(), ULocale.getDefault(Category.FORMAT), CHINA_ZONE);

        // Set 0 to millisecond field
        this.set(MILLISECOND, 0);

        // Then, set the given field values.
        this.set(ERA, era);
        this.set(YEAR, year);
        this.set(MONTH, month);
        this.set(IS_LEAP_MONTH, isLeapMonth);
        this.set(DATE, date);
        this.set(HOUR_OF_DAY, hour);
        this.set(MINUTE, minute);
        this.set(SECOND, second);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> based on the current time in the default time zone
     * with the given locale.
     *
     * @param aLocale The given locale
     * @stable ICU 4.0
     */
    public ChineseCalendar(Locale aLocale) {
        this(TimeZone.forLocaleOrDefault(aLocale), ULocale.forLocale(aLocale), CHINA_ZONE);
    }

    /**
     * Construct a <code>ChineseCalendar</code> based on the current time in the given time zone
     * with the default <code>FORMAT</code> locale.
     *
     * @param zone the given time zone
     * @see Category#FORMAT
     * @stable ICU 4.0
     */
    public ChineseCalendar(TimeZone zone) {
        this(zone, ULocale.getDefault(Category.FORMAT), CHINA_ZONE);
    }

    /**
     * Construct a <code>ChineseCalendar</code> based on the current time in the given time zone
     * with the given locale.
     *
     * @param zone the given time zone
     * @param aLocale the given locale
     * @stable ICU 2.8
     */
    public ChineseCalendar(TimeZone zone, Locale aLocale) {
        this(zone, ULocale.forLocale(aLocale), CHINA_ZONE);
    }

    /**
     * Constructs a <code>ChineseCalendar</code> based on the current time in the default time zone
     * with the given locale.
     *
     * @param locale the given ulocale
     * @stable ICU 4.0
     */
    public ChineseCalendar(ULocale locale) {
        this(TimeZone.forULocaleOrDefault(locale), locale, CHINA_ZONE);
    }

    /**
     * Construct a <code>ChineseCalendar</code> based on the current time with the given time zone
     * with the given locale.
     *
     * @param zone the given time zone
     * @param locale the given ulocale
     * @stable ICU 3.2
     */
    public ChineseCalendar(TimeZone zone, ULocale locale) {
        this(zone, locale, CHINA_ZONE);
    }

    /**
     * Construct a <code>ChineseCalenar</code> based on the current time with the given time zone,
     * the locale, the epoch year and the time zone used for astronomical calculation.
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Deprecated
    protected ChineseCalendar(TimeZone zone, ULocale locale, TimeZone zoneAstroCalc) {
        super(zone, locale);
        this.zoneAstro = zoneAstroCalc;
        setTimeInMillis(System.currentTimeMillis());
    }

    // ------------------------------------------------------------------
    // Public constants
    // ------------------------------------------------------------------

    /**
     * Field indicating whether or not the current month is a leap month. Should have a value of 0
     * for non-leap months, and 1 for leap months.
     *
     * @stable ICU 2.8
     */
    // public static int IS_LEAP_MONTH = BASE_FIELD_COUNT;

    // ------------------------------------------------------------------
    // Calendar framework
    // ------------------------------------------------------------------

    /**
     * Array defining the limits of field values for this class. Field limits which are invariant
     * with respect to calendar system and defined by Calendar are left blank.
     *
     * <p>Notes:
     *
     * <p>ERA 5000000 / 60 = 83333.
     *
     * <p>MONTH There are 12 or 13 lunar months in a year. However, we always number them 0..11,
     * with an intercalated, identically numbered leap month, when necessary.
     *
     * <p>DAY_OF_YEAR In a non-leap year there are 353, 354, or 355 days. In a leap year there are
     * 383, 384, or 385 days.
     *
     * <p>WEEK_OF_YEAR The least maximum occurs if there are 353 days in the year, and the first 6
     * are the last week of the previous year. Then we have 49 full weeks and 4 days in the last
     * week: 6 + 49*7 + 4 = 353. So the least maximum is 50. The maximum occurs if there are 385
     * days in the year, and WOY 1 extends 6 days into the prior year. Then there are 54 full weeks,
     * and 6 days in the last week: 1 + 54*7 + 6 = 385. The 6 days of the last week will fall into
     * WOY 1 of the next year. Maximum is 55.
     *
     * <p>WEEK_OF_MONTH In a 29 day month, if the first 7 days make up week 1 that leaves 3 full
     * weeks and 1 day at the end. The least maximum is thus 5. In a 30 days month, if the previous
     * 6 days belong WOM 1 of this month, we have 4 full weeks and 1 days at the end (which
     * technically will be WOM 1 of the next month, but will be reported by time->fields and hence
     * by getActualMaximum as WOM 6 of this month). Maximum is 6.
     *
     * <p>DAY_OF_WEEK_IN_MONTH In a 29 or 30 day month, there are 4 full weeks plus 1 or 2 days at
     * the end, so the maximum is always 5.
     */
    private static final int LIMITS[][] = {
        // Minimum  Greatest    Least  Maximum
        //           Minimum  Maximum
        {1, 1, 83333, 83333}, // ERA
        {1, 1, 60, 60}, // YEAR
        {0, 0, 11, 11}, // MONTH
        {1, 1, 50, 55}, // WEEK_OF_YEAR
        {
            /*                                  */
        }, // WEEK_OF_MONTH
        {1, 1, 29, 30}, // DAY_OF_MONTH
        {1, 1, 353, 385}, // DAY_OF_YEAR
        {
            /*                                  */
        }, // DAY_OF_WEEK
        {-1, -1, 5, 5}, // DAY_OF_WEEK_IN_MONTH
        {
            /*                                  */
        }, // AM_PM
        {
            /*                                  */
        }, // HOUR
        {
            /*                                  */
        }, // HOUR_OF_DAY
        {
            /*                                  */
        }, // MINUTE
        {
            /*                                  */
        }, // SECOND
        {
            /*                                  */
        }, // MILLISECOND
        {
            /*                                  */
        }, // ZONE_OFFSET
        {
            /*                                  */
        }, // DST_OFFSET
        {-5000000, -5000000, 5000000, 5000000}, // YEAR_WOY
        {
            /*                                  */
        }, // DOW_LOCAL
        {-5000000, -5000000, 5000000, 5000000}, // EXTENDED_YEAR
        {
            /*                                  */
        }, // JULIAN_DAY
        {
            /*                                  */
        }, // MILLISECONDS_IN_DAY
        {0, 0, 1, 1}, // IS_LEAP_MONTH
        {0, 0, 11, 12}, // ORDINAL_MONTH
    };

    /**
     * Override Calendar to return the limit value for the given field.
     *
     * @stable ICU 2.8
     */
    @Override
    protected int handleGetLimit(int field, int limitType) {
        return LIMITS[field][limitType];
    }

    /**
     * Implement abstract Calendar method to return the extended year defined by the current fields.
     * This will use either the ERA and YEAR field as the cycle and year-of-cycle, or the
     * EXTENDED_YEAR field as the continuous year count, depending on which is newer.
     *
     * @stable ICU 2.8
     */
    @Override
    protected int handleGetExtendedYear() {
        int year;
        if (newestStamp(ERA, YEAR, UNSET) <= getStamp(EXTENDED_YEAR)) {
            year = internalGet(EXTENDED_YEAR, 1); // Default to year 1
        } else {
            int cycle = internalGet(ERA, 1) - 1; // 0-based cycle
            // adjust to the instance specific epoch
            year = cycle * 60 + internalGet(YEAR, 1) + CYCLE_EPOCH - CHINESE_EPOCH_YEAR;
        }
        return year;
    }

    /**
     * Override Calendar method to return the number of days in the given extended year and month.
     *
     * <p>Note: This method also reads the IS_LEAP_MONTH field to determine whether or not the given
     * month is a leap month.
     *
     * @stable ICU 2.8
     */
    @Override
    protected int handleGetMonthLength(int extendedYear, int month) {
        int isLeapMonth = internalGet(IS_LEAP_MONTH);
        return handleGetMonthLengthWithLeap(extendedYear, month, isLeapMonth);
    }

    private int handleGetMonthLengthWithLeap(int extendedYear, int month, int isLeap) {
        int thisStart =
                handleComputeMonthStartWithLeap(extendedYear, month, isLeap)
                        - EPOCH_JULIAN_DAY
                        + 1; // Julian day -> local days
        int nextStart = newMoonNear(thisStart + SYNODIC_GAP, true);
        return nextStart - thisStart;
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 4.2
     */
    @Override
    protected DateFormat handleGetDateFormat(String pattern, String override, ULocale locale) {
        // Note: ICU 50 or later versions no longer use ChineseDateFormat.
        // The super class's handleGetDateFormat will create an instance of
        // SimpleDateFormat which supports Chinese calendar date formatting
        // since ICU 49.

        // return new ChineseDateFormat(pattern, override, locale);
        return super.handleGetDateFormat(pattern, override, locale);
    }

    /** Field resolution table that incorporates IS_LEAP_MONTH. */
    static final int[][][] CHINESE_DATE_PRECEDENCE = {
        {
            {DAY_OF_MONTH},
            {WEEK_OF_YEAR, DAY_OF_WEEK},
            {WEEK_OF_MONTH, DAY_OF_WEEK},
            {DAY_OF_WEEK_IN_MONTH, DAY_OF_WEEK},
            {WEEK_OF_YEAR, DOW_LOCAL},
            {WEEK_OF_MONTH, DOW_LOCAL},
            {DAY_OF_WEEK_IN_MONTH, DOW_LOCAL},
            {DAY_OF_YEAR},
            {RESOLVE_REMAP | DAY_OF_MONTH, IS_LEAP_MONTH},
        },
        {
            {WEEK_OF_YEAR},
            {WEEK_OF_MONTH},
            {DAY_OF_WEEK_IN_MONTH},
            {RESOLVE_REMAP | DAY_OF_WEEK_IN_MONTH, DAY_OF_WEEK},
            {RESOLVE_REMAP | DAY_OF_WEEK_IN_MONTH, DOW_LOCAL},
        },
    };

    /**
     * Override Calendar to add IS_LEAP_MONTH to the field resolution table.
     *
     * @stable ICU 2.8
     */
    @Override
    protected int[][][] getFieldResolutionTable() {
        return CHINESE_DATE_PRECEDENCE;
    }

    /**
     * Adjust this calendar to be delta months before or after a given start position, pinning the
     * day of month if necessary. The start position is given as a local days number for the start
     * of the month and a day-of-month. Used by add() and roll().
     *
     * @param newMoon the local days of the first day of the month of the start position (days after
     *     January 1, 1970 0:00 Asia/Shanghai)
     * @param dom the 1-based day-of-month of the start position
     * @param delta the number of months to move forward or backward from the start position
     */
    private void offsetMonth(int newMoon, int dom, int delta) {
        // Move to the middle of the month before our target month.
        newMoon += (int) (CalendarAstronomer.SYNODIC_MONTH * (delta - 0.5));

        // Search forward to the target month's new moon
        newMoon = newMoonNear(newMoon, true);

        // Find the target dom
        int jd = newMoon + EPOCH_JULIAN_DAY - 1 + dom;

        // Pin the dom.  In this calendar all months are 29 or 30 days
        // so pinning just means handling dom 30.
        if (dom > 29) {
            set(JULIAN_DAY, jd - 1);
            // TODO Fix this.  We really shouldn't ever have to
            // explicitly call complete().  This is either a bug in
            // this method, in ChineseCalendar, or in
            // Calendar.getActualMaximum().  I suspect the last.
            complete();
            if (getActualMaximum(DAY_OF_MONTH) >= dom) {
                set(JULIAN_DAY, jd);
            }
        } else {
            set(JULIAN_DAY, jd);
        }
    }

    /**
     * Override Calendar to handle leap months properly.
     *
     * @stable ICU 2.8
     */
    @Override
    public void add(int field, int amount) {
        switch (field) {
            case MONTH:
            case ORDINAL_MONTH:
                if (amount != 0) {
                    int dom = get(DAY_OF_MONTH);
                    int day = get(JULIAN_DAY) - EPOCH_JULIAN_DAY; // Get local day
                    int moon = day - dom + 1; // New moon
                    offsetMonth(moon, dom, amount);
                }
                break;
            default:
                super.add(field, amount);
                break;
        }
    }

    /**
     * Override Calendar to handle leap months properly.
     *
     * @stable ICU 2.8
     */
    @Override
    public void roll(int field, int amount) {
        switch (field) {
            case MONTH:
            case ORDINAL_MONTH:
                if (amount != 0) {
                    int dom = get(DAY_OF_MONTH);
                    int day = get(JULIAN_DAY) - EPOCH_JULIAN_DAY; // Get local day
                    int moon = day - dom + 1; // New moon (start of this month)

                    // Note throughout the following:  Months 12 and 1 are never
                    // followed by a leap month (D&R p. 185).

                    // Compute the adjusted month number m.  This is zero-based
                    // value from 0..11 in a non-leap year, and from 0..12 in a
                    // leap year.
                    int m = get(MONTH); // 0-based month
                    if (hasLeapMonthBetweenWinterSolstices) { // (member variable)
                        if (get(IS_LEAP_MONTH) == 1) {
                            ++m;
                        } else {
                            // Check for a prior leap month.  (In the
                            // following, month 0 is the first month of the
                            // year.)  Month 0 is never followed by a leap
                            // month, and we know month m is not a leap month.
                            // moon1 will be the start of month 0 if there is
                            // no leap month between month 0 and month m;
                            // otherwise it will be the start of month 1.
                            int moon1 = moon - (int) (CalendarAstronomer.SYNODIC_MONTH * (m - 0.5));
                            moon1 = newMoonNear(moon1, true);
                            if (isLeapMonthBetween(moon1, moon)) {
                                ++m;
                            }
                        }
                    }

                    // Now do the standard roll computation on m, with the
                    // allowed range of 0..n-1, where n is 12 or 13.
                    int n = hasLeapMonthBetweenWinterSolstices ? 13 : 12; // Months in this year
                    int newM = (m + amount) % n;
                    if (newM < 0) {
                        newM += n;
                    }

                    if (newM != m) {
                        offsetMonth(moon, dom, newM - m);
                    }
                }
                break;
            default:
                super.roll(field, amount);
                break;
        }
    }

    // ------------------------------------------------------------------
    // Support methods and constants
    // ------------------------------------------------------------------

    /** The start year of the Chinese calendar, 1CE. */
    private static final int CHINESE_EPOCH_YEAR = 1; // Gregorian year

    /**
     * The start year of the Chinese calendar for the cycle calculation, the 61st year of the reign
     * of Huang Di. Some sources use the first year of his reign, ERA (cycle) values one greater.
     */
    private static final int CYCLE_EPOCH = -2636; // Gregorian year

    /**
     * The time zone used for performing astronomical computations. Some sources use a different
     * historically accurate offset of GMT+7:45:40 for years before 1929; we do not do this.
     */
    private static final TimeZone CHINA_ZONE =
            new SimpleTimeZone(8 * ONE_HOUR, "CHINA_ZONE").freeze();

    /**
     * Value to be added or subtracted from the local days of a new moon to get close to the next or
     * prior new moon, but not cross it. Must be >= 1 and < CalendarAstronomer.SYNODIC_MONTH.
     */
    private static final int SYNODIC_GAP = 25;

    /**
     * Convert local days to UTC epoch milliseconds. This is not an accurate conversion in terms
     * that getTimezoneOffset takes the milliseconds in GMT (not local time). In theory, more
     * accurate algorithm can be implemented but practically we do not need to go through that
     * complication as long as the historically timezone changes did not happen around the 'tricky'
     * new moon (new moon around the midnight).
     *
     * @param days days after January 1, 1970 0:00 in the astronomical base zone
     * @return milliseconds after January 1, 1970 0:00 GMT
     */
    private final long daysToMillis(int days) {
        long millis = days * ONE_DAY;
        return millis - zoneAstro.getOffset(millis);
    }

    /**
     * Convert UTC epoch milliseconds to local days.
     *
     * @param millis milliseconds after January 1, 1970 0:00 GMT
     * @return days days after January 1, 1970 0:00 in the astronomical base zone
     */
    private final int millisToDays(long millis) {
        return (int) floorDivide(millis + zoneAstro.getOffset(millis), ONE_DAY);
    }

    // ------------------------------------------------------------------
    // Astronomical computations
    // ------------------------------------------------------------------

    /**
     * Return the major solar term on or after December 15 of the given Gregorian year, that is, the
     * winter solstice of the given year. Computations are relative to Asia/Shanghai time zone.
     *
     * @param gyear a Gregorian year
     * @return days after January 1, 1970 0:00 Asia/Shanghai of the winter solstice of the given
     *     year
     */
    private int winterSolstice(int gyear) {

        long cacheValue = winterSolsticeCache.get(gyear);

        if (cacheValue == CalendarCache.EMPTY) {
            // In books December 15 is used, but it fails for some years
            // using our algorithms, e.g.: 1298 1391 1492 1553 1560.  That
            // is, winterSolstice(1298) starts search at Dec 14 08:00:00
            // PST 1298 with a final result of Dec 14 10:31:59 PST 1299.
            long ms =
                    daysToMillis(
                            computeGregorianMonthStart(gyear, DECEMBER) + 1 - EPOCH_JULIAN_DAY);

            // Winter solstice is 270 degrees solar longitude aka Dongzhi
            long solarLong =
                    (new CalendarAstronomer(ms))
                            .getSunTime(CalendarAstronomer.WINTER_SOLSTICE, true);
            cacheValue = millisToDays(solarLong);
            winterSolsticeCache.put(gyear, cacheValue);
        }
        return (int) cacheValue;
    }

    /**
     * Return the closest new moon to the given date, searching either forward or backward in time.
     *
     * @param days days after January 1, 1970 0:00 Asia/Shanghai
     * @param after if true, search for a new moon on or after the given date; otherwise, search for
     *     a new moon before it
     * @return days after January 1, 1970 0:00 Asia/Shanghai of the nearest new moon after or before
     *     <code>days</code>
     */
    private int newMoonNear(int days, boolean after) {
        long newMoon =
                (new CalendarAstronomer(daysToMillis(days)))
                        .getMoonTime(CalendarAstronomer.NEW_MOON, after);

        return millisToDays(newMoon);
    }

    /**
     * Return the nearest integer number of synodic months between two dates.
     *
     * @param day1 days after January 1, 1970 0:00 Asia/Shanghai
     * @param day2 days after January 1, 1970 0:00 Asia/Shanghai
     * @return the nearest integer number of months between day1 and day2
     */
    private int synodicMonthsBetween(int day1, int day2) {
        return (int) Math.round((day2 - day1) / CalendarAstronomer.SYNODIC_MONTH);
    }

    /**
     * Return the major solar term on or before a given date. This will be an integer from 1..12,
     * with 1 corresponding to 330 degrees, 2 to 0 degrees, 3 to 30 degrees,..., and 12 to 300
     * degrees.
     *
     * @param days days after January 1, 1970 0:00 Asia/Shanghai
     */
    private int majorSolarTerm(int days) {
        // Compute (floor(solarLongitude / (pi/6)) + 2) % 12
        int term =
                ((int)
                                        Math.floor(
                                                6
                                                        * (new CalendarAstronomer(
                                                                        daysToMillis(days)))
                                                                .getSunLongitude()
                                                        / Math.PI)
                                + 2)
                        % 12;
        if (term < 1) {
            term += 12;
        }
        return term;
    }

    /**
     * Return true if the given month lacks a major solar term.
     *
     * @param newMoon days after January 1, 1970 0:00 Asia/Shanghai of a new moon
     */
    private boolean hasNoMajorSolarTerm(int newMoon) {

        int mst = majorSolarTerm(newMoon);
        int nmn = newMoonNear(newMoon + SYNODIC_GAP, true);
        int mstt = majorSolarTerm(nmn);
        return mst == mstt;
        /*
        return majorSolarTerm(newMoon) ==
            majorSolarTerm(newMoonNear(newMoon + SYNODIC_GAP, true));
        */
    }

    // ------------------------------------------------------------------
    // Time to fields
    // ------------------------------------------------------------------

    /**
     * Return true if there is a leap month on or after month newMoon1 and at or before month
     * newMoon2.
     *
     * @param newMoon1 days after January 1, 1970 0:00 astronomical base zone of a new moon
     * @param newMoon2 days after January 1, 1970 0:00 astronomical base zone of a new moon
     */
    private boolean isLeapMonthBetween(int newMoon1, int newMoon2) {

        // This is only needed to debug the timeOfAngle divergence bug.
        // Remove this later. Liu 11/9/00
        // DEBUG
        if (synodicMonthsBetween(newMoon1, newMoon2) >= 50) {
            throw new IllegalArgumentException(
                    "isLeapMonthBetween(" + newMoon1 + ", " + newMoon2 + "): Invalid parameters");
        }

        return (newMoon2 >= newMoon1)
                && (isLeapMonthBetween(newMoon1, newMoonNear(newMoon2 - SYNODIC_GAP, false))
                        || hasNoMajorSolarTerm(newMoon2));
    }

    /**
     * Override Calendar to compute several fields specific to the Chinese calendar system. These
     * are:
     *
     * <ul>
     *   <li>ERA
     *   <li>YEAR
     *   <li>MONTH
     *   <li>DAY_OF_MONTH
     *   <li>DAY_OF_YEAR
     *   <li>EXTENDED_YEAR
     * </ul>
     *
     * The DAY_OF_WEEK and DOW_LOCAL fields are already set when this method is called. The
     * getGregorianXxx() methods return Gregorian calendar equivalents for the given Julian day.
     *
     * <p>Compute the ChineseCalendar-specific field IS_LEAP_MONTH.
     *
     * @stable ICU 2.8
     */
    @Override
    protected void handleComputeFields(int julianDay) {
        int days = julianDay - EPOCH_JULIAN_DAY; // local days
        int gyear = getGregorianYear();
        int gmonth = getGregorianMonth();
        MonthInfo info = computeMonthInfo(days, gyear);

        // Extended year and cycle year is based on the epoch year
        int extended_year = gyear - CHINESE_EPOCH_YEAR;
        int cycle_year = gyear - CYCLE_EPOCH;
        if (info.month < 10
                || // TODO(ICU-23198) < 10 or < 11 ????
                gmonth >= JULY) {
            extended_year++;
            cycle_year++;
        }
        int dayOfMonth = days - info.thisMoon + 1;

        // 0->0,60  1->1,1  60->1,60  61->2,1  etc.
        int[] yearOfCycle = new int[1];
        int cycle = floorDivide(cycle_year - 1, 60, yearOfCycle);

        // Days will be before the first new year we compute if this
        // date is in month 11, leap 11, 12.  There is never a leap 12.
        // New year computations are cached so this should be cheap in
        // the long run.
        int newYear = newYear(gyear);
        if (days < newYear) {
            newYear = newYear(gyear - 1);
        }

        hasLeapMonthBetweenWinterSolstices = info.hasLeapMonthBetweenWinterSolstices;
        internalSet(EXTENDED_YEAR, extended_year);
        internalSet(ERA, cycle + 1);
        internalSet(YEAR, yearOfCycle[0] + 1);
        internalSet(MONTH, info.month); // Convert from 1-based to 0-based
        internalSet(ORDINAL_MONTH, info.ordinalMonth);
        internalSet(DAY_OF_MONTH, dayOfMonth);
        internalSet(IS_LEAP_MONTH, info.isLeapMonth ? 1 : 0);
        internalSet(DAY_OF_YEAR, days - newYear + 1);
    }

    class MonthInfo {
        int month;
        int ordinalMonth;
        int thisMoon;
        boolean isLeapMonth;
        boolean hasLeapMonthBetweenWinterSolstices;

        MonthInfo(
                int month,
                int ordinalMonth,
                int thisMoon,
                boolean isLeapMonth,
                boolean hasLeapMonthBetweenWinterSolstices) {
            this.month = month;
            this.ordinalMonth = ordinalMonth;
            this.thisMoon = thisMoon;
            this.isLeapMonth = isLeapMonth;
            this.hasLeapMonthBetweenWinterSolstices = hasLeapMonthBetweenWinterSolstices;
        }
    }
    ;

    private MonthInfo computeMonthInfo(int days, int gyear) {
        // Find the winter solstices before and after the target date.
        // These define the boundaries of this Chinese year, specifically,
        // the position of month 11, which always contains the solstice.
        // We want solsticeBefore <= date < solsticeAfter.
        int solsticeBefore;
        int solsticeAfter = winterSolstice(gyear);
        if (days < solsticeAfter) {
            solsticeBefore = winterSolstice(gyear - 1);
        } else {
            solsticeBefore = solsticeAfter;
            solsticeAfter = winterSolstice(gyear + 1);
        }

        // Find the start of the month after month 11.  This will be either
        // the prior month 12 or leap month 11 (very rare).  Also find the
        // start of the following month 11.
        int firstMoon = newMoonNear(solsticeBefore + 1, true);
        int lastMoon = newMoonNear(solsticeAfter + 1, false);
        int thisMoon = newMoonNear(days + 1, false); // Start of this month

        boolean hasLeapMonthBetweenWinterSolstices =
                synodicMonthsBetween(firstMoon, lastMoon) == 12;

        int month = synodicMonthsBetween(firstMoon, thisMoon);
        int theNewYear = newYear(gyear);
        if (days < theNewYear) {
            theNewYear = newYear(gyear - 1);
        }
        if (hasLeapMonthBetweenWinterSolstices && isLeapMonthBetween(firstMoon, thisMoon)) {
            month--;
        }
        if (month < 1) {
            month += 12;
        }
        int ordinalMonth = synodicMonthsBetween(theNewYear, thisMoon);
        if (ordinalMonth < 0) {
            ordinalMonth += 12;
        }

        boolean isLeapMonth =
                hasLeapMonthBetweenWinterSolstices
                        && hasNoMajorSolarTerm(thisMoon)
                        && !isLeapMonthBetween(
                                firstMoon, newMoonNear(thisMoon - SYNODIC_GAP, false));

        return new MonthInfo(
                month - 1, ordinalMonth, thisMoon, isLeapMonth, hasLeapMonthBetweenWinterSolstices);
    }

    // ------------------------------------------------------------------
    // Fields to time
    // ------------------------------------------------------------------

    /**
     * Return the Chinese new year of the given Gregorian year.
     *
     * @param gyear a Gregorian year
     * @return days after January 1, 1970 0:00 astronomical base zone of the Chinese new year of the
     *     given year (this will be a new moon)
     */
    private int newYear(int gyear) {

        long cacheValue = newYearCache.get(gyear);

        if (cacheValue == CalendarCache.EMPTY) {

            int solsticeBefore = winterSolstice(gyear - 1);
            int solsticeAfter = winterSolstice(gyear);
            int newMoon1 = newMoonNear(solsticeBefore + 1, true);
            int newMoon2 = newMoonNear(newMoon1 + SYNODIC_GAP, true);
            int newMoon11 = newMoonNear(solsticeAfter + 1, false);

            if (synodicMonthsBetween(newMoon1, newMoon11) == 12
                    && (hasNoMajorSolarTerm(newMoon1) || hasNoMajorSolarTerm(newMoon2))) {
                cacheValue = newMoonNear(newMoon2 + SYNODIC_GAP, true);
            } else {
                cacheValue = newMoon2;
            }

            newYearCache.put(gyear, cacheValue);
        }
        return (int) cacheValue;
    }

    /**
     * Return the Julian day number of day before the first day of the given month in the given
     * extended year.
     *
     * <p>Note: This method reads the IS_LEAP_MONTH field to determine whether the given month is a
     * leap month.
     *
     * @param eyear the extended year
     * @param month the zero-based month. The month is also determined by reading the IS_LEAP_MONTH
     *     field.
     * @return the Julian day number of the day before the first day of the given month and year
     * @stable ICU 2.8
     */
    @Override
    protected int handleComputeMonthStart(int eyear, int month, boolean useMonth) {
        int isLeapMonth = 0;
        if (useMonth) {
            isLeapMonth = internalGet(IS_LEAP_MONTH);
        }
        return handleComputeMonthStartWithLeap(eyear, month, isLeapMonth);
    }

    private int handleComputeMonthStartWithLeap(int eyear, int month, int isLeapMonth) {

        // If the month is out of range, adjust it into range, and
        // modify the extended year value accordingly.
        if (month < 0 || month > 11) {
            int[] rem = new int[1];
            eyear += floorDivide(month, 12, rem);
            month = rem[0];
        }

        int gyear = eyear; // Gregorian year
        int newYear = newYear(gyear);
        int newMoon = newMoonNear(newYear + month * 29, true);

        int julianDay = newMoon + EPOCH_JULIAN_DAY;

        computeGregorianFields(julianDay);

        // This will modify the MONTH and IS_LEAP_MONTH fields (only)
        MonthInfo info = computeMonthInfo(newMoon, getGregorianYear());

        if (month != info.month || info.isLeapMonth != (isLeapMonth != 0)) {
            newMoon = newMoonNear(newMoon + SYNODIC_GAP, true);
            julianDay = newMoon + EPOCH_JULIAN_DAY;
        }

        return julianDay - 1;
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 3.8
     */
    @Override
    public String getType() {
        return "chinese";
    }

    /**
     * {@inheritDoc}
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Override
    @Deprecated
    public boolean haveDefaultCentury() {
        return false;
    }

    /** Override readObject. */
    private void readObject(ObjectInputStream stream) throws IOException, ClassNotFoundException {
        zoneAstro = CHINA_ZONE;

        stream.defaultReadObject();

        /* set up the transient caches... */
        winterSolsticeCache = new CalendarCache();
        newYearCache = new CalendarCache();
    }

    // -------------------------------------------------------------------------
    // Temporal Calendar API.
    // -------------------------------------------------------------------------
    /**
     * {@icu} Returns true if the date is in a leap year. Recalculate the current time field values
     * if the time value has been changed by a call to setTime(). This method is semantically const,
     * but may alter the object in memory. A "leap year" is a year that contains more days than
     * other years (for solar or lunar calendars) or more months than other years (for lunisolar
     * calendars like Hebrew or Chinese), as defined in the ECMAScript Temporal proposal.
     *
     * @return true if the date in the fields is in a Temporal proposal defined leap year. False
     *     otherwise.
     * @stable ICU 74
     */
    @Override
    public boolean inTemporalLeapYear() {
        return getActualMaximum(DAY_OF_YEAR) > 360;
    }

    private static String[] gTemporalLeapMonthCodes = {
        "M01L", "M02L", "M03L", "M04L", "M05L", "M06L", "M07L", "M08L", "M09L", "M10L", "M11L",
        "M12L"
    };

    /**
     * Gets The Temporal monthCode value corresponding to the month for the date. The value is a
     * string identifier that starts with the literal grapheme "M" followed by two graphemes
     * representing the zero-padded month number of the current month in a normal (non-leap) year
     * and suffixed by an optional literal grapheme "L" if this is a leap month in a lunisolar
     * calendar. For the Chinese calendar, the values are "M01" .. "M12" for non-leap year and * in
     * leap year with another monthCode in "M01L" .. "M12L".
     *
     * @return One of 24 possible strings in {"M01".."M12", "M01L".."M12L"}.
     * @stable ICU 74
     */
    @Override
    public String getTemporalMonthCode() {
        // We need to call get, not internalGet, to force the calculation
        // from ORDINAL_MONTH.
        int is_leap = get(IS_LEAP_MONTH);
        if (is_leap != 0) {
            return gTemporalLeapMonthCodes[get(MONTH)];
        }
        return super.getTemporalMonthCode();
    }

    /**
     * Sets The Temporal monthCode which is a string identifier that starts with the literal
     * grapheme "M" followed by two graphemes representing the zero-padded month number of the
     * current month in a normal (non-leap) year and suffixed by an optional literal grapheme "L" if
     * this is a leap month in a lunisolar calendar. For the Chinese calendar, the values are "M01"
     * .. "M12" for non-leap year and in leap year with another monthCode in "M01L" .. "M12L".
     *
     * @param temporalMonth One of 25 possible strings in {"M01".. "M12", "M13", "M01L", "M12L"}.
     * @stable ICU 74
     */
    @Override
    public void setTemporalMonthCode(String temporalMonth) {
        if (temporalMonth.length() != 4
                || temporalMonth.charAt(0) != 'M'
                || temporalMonth.charAt(3) != 'L') {
            set(IS_LEAP_MONTH, 0);
            super.setTemporalMonthCode(temporalMonth);
            return;
        }
        for (int m = 0; m < gTemporalLeapMonthCodes.length; m++) {
            if (temporalMonth.equals(gTemporalLeapMonthCodes[m])) {
                set(MONTH, m);
                set(IS_LEAP_MONTH, 1);
                return;
            }
        }
        throw new IllegalArgumentException("Incorrect temporal Month code: " + temporalMonth);
    }

    // -------------------------------------------------------------------------
    // End of Temporal Calendar API
    // -------------------------------------------------------------------------

    /**
     * {@inheritDoc}
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Override
    @Deprecated
    protected int internalGetMonth() {
        if (resolveFields(MONTH_PRECEDENCE) == MONTH) {
            return internalGet(MONTH);
        }
        Calendar temp = clone();
        temp.set(Calendar.MONTH, 0);
        temp.set(Calendar.IS_LEAP_MONTH, 0);
        temp.set(Calendar.DATE, 1);
        // Calculate the MONTH and IS_LEAP_MONTH by adding number of months.
        temp.roll(Calendar.MONTH, internalGet(Calendar.ORDINAL_MONTH));
        internalSet(Calendar.IS_LEAP_MONTH, temp.get(Calendar.IS_LEAP_MONTH));
        int month = temp.get(Calendar.MONTH);
        internalSet(Calendar.MONTH, month);
        return month;
    }

    /**
     * {@inheritDoc}
     *
     * @internal
     * @deprecated This API is ICU internal only.
     */
    @Override
    @Deprecated
    protected int internalGetMonth(int defaultValue) {
        if (resolveFields(MONTH_PRECEDENCE) == MONTH) {
            return internalGet(MONTH, defaultValue);
        }
        return internalGetMonth();
    }

    /**
     * {@inheritDoc}
     *
     * @stable ICU 2.8
     */
    @Override
    public int getActualMaximum(int field) {
        if (field == DAY_OF_MONTH) {
            Calendar cal = clone();
            cal.setLenient(true);
            cal.prepareGetActual(field, false);
            int eyear = cal.get(EXTENDED_YEAR);
            int month = cal.get(MONTH);
            int isLeap = cal.get(IS_LEAP_MONTH);

            return handleGetMonthLengthWithLeap(eyear, month, isLeap);
        }
        return super.getActualMaximum(field);
    }

    /*
    private static CalendarFactory factory;
    public static CalendarFactory factory() {
        if (factory == null) {
            factory = new CalendarFactory() {
                public Calendar create(TimeZone tz, ULocale loc) {
                    return new ChineseCalendar(tz, loc);
                }

                public String factoryName() {
                    return "Chinese";
                }
            };
        }
        return factory;
    }
    */
}
